From ACT Wiki
The statutory duty (in the UK) imposed on the Scheme Actuary, the Scheme Auditor, trustees, the employer and various other named parties to advise the Pensions Regulator immediately in writing if they have reasonable cause to believe there is a material problem with an Occupational Pension Scheme. Others may do so, but have no statutory duty to do so.
The duty was originally introduced under the Pensions Act 1995 and extended under the Pensions Act 2004.
2. Other misconduct.
More generally, disclosing misconduct to the relevant authorities, especially when disclosed by an insider.